Neuroblastoma illustrates the striking clinical heterogeneity that one tumor histotype can encompass, with stage 4S patients undergoing spontaneous tumor regression and high-risk patients exhibiting significant mortality. Our laboratory recently identified LIN28B, an RNA binding protein that inhibits the let-7 tumor suppressor microRNA family and binds mRNAs directly, as an oncogenic driver in neuroblastoma. While its roles in metabolism and embryonic development are becoming increasingly well-understood, how it promotes oncogene- sis is less clear. We have shown that LIN28B drives expression of the Ras-related protein RAN and Aurora kinase A (AURKA), to promote neuroblastoma proliferation. We also have evidence indicating that LIN28B promotes stemless related gene signatures in neuroblastoma, raising the possibility that its function in promoting self-renewal in normal development may also serve an oncogenic role. This Mentored Career Development proposal will test the hypothesis that LIN28B, in conjunction with RAN and AURKA, promotes cell proliferation and self-renewal to drive neuroblastoma aggression. First, we will determine the mechanisms by which LIN28B promotes self-renewal. Second, we will dissect the contribution of the downstream LIN28B targets RAN and AURKA to cell proliferation and self-renewal. In the final aim, we will test the hypothesis that LIN28B binding to mRNAs, including mRNAs of the RAN signaling network, provides one mechanism by which it exerts its oncogenic function. This K08 Award will broaden my scientific repertoire and provide an outstanding basis for a career in basic and translational oncology. First, in Aims 1 and 2, I will develop new expertise on the role of LIN28B/let-7 in mediating self-renewal, a hallmark of cancer that may represent an eventual therapeutic vulnerability but that re- quires further study. Second, I will master RNA-Seq and related technologies, using it to generate and test hypotheses; in Aim 1, I will use RNA-Seq to unveil the pathways LIN28B utilizes to regulate self-renewal. Finally, in Aim 3, I will develop expertise in utilizing CLIP-Seq, a high-throughput technology that identifies RNAs to which RNA binding proteins bind. This will further our understanding of coding and non-coding RNAs influenced by LIN28B and may improve our understanding of how other RNA binding proteins function. This work will be completed under the outstanding mentorship of Dr. John Maris and an Advisory Committee, comprised of Drs. Anil Rustgi, Celeste Simon, Andrei Thomas-Tikhonenko, Tom Look, and Sharon Diskin. Collectively, this committee possesses expertise in cancer genetics, RNA binding proteins, microRNAs, stem cell biology, bioinformatics, and animal models of disease. By studying this key pathway in neuroblastoma, I aim to lay the basis for its eventual therapeutic manipulation and generate novel insights to further our understanding of both pediatric and adult malignancies. In summary, both the scientific and educational components of this grant will strengthen my scientific foundation, allowing me to launch an independent research career.